EDuke32 Modifications

Disclaimer: This list of mods and TCs is by no means exhaustive. There are many more great user made addons to try out on the internet, what is shown in this list comprises solely of content that the respective mod makers themselves have put up.
What is shown here isn't necessarily the best (although some of it is, and all of it is high quality), it's just that the people who made them actually bothered to make an entry here.

Large Projects

The AMC TC is a multi-character TC and gameplay modification. There are 9 characters to choose between, each with different weapon sets and items. Fight through the solar system against Duke's old enemies as well as other dark forces that each plan something unpleasant for Earth and Mars. Episode 1 and 2 have been released.

What will come to be an alternate-universe Duke Nukem story revolving around a pivotal point in the history of Duke Nukem and the Aliens he has faced since the original Duke Nukem 3D. Duke is no longer working alone in his quest, as his enemies ramp up their power and allegiances substantially, as well as their intelligence to a point. Play as up to 15 different characters, with the ability to use multiple characters in the same party, unlike in Hexen (and more like a real RPG). Monsters are more interactive and to a point more intelligent, able to grab items like health and armor, get damaged by slime and other hazards, and even pick up power-ups to make them deadlier in combat. Find money laying around or get it out of your characters' ATM accounts, and use it to buy new items from shops or other NPCs. Voice Acting is also present.

BloodCM is a recreation of Blood (by Monolith Productions) for EDuke32 to bring all the fun and action of Blood to the EDuke32 port. This mod will be more powerful in the future, considering EDuke32 keeps getting better and better.
Big thanks: The Lezing, DeeperThought, DefaultDan(97), Zykov Eddy, --DarkSoL--, Yura_evil, KLIMaka, XTHX2, Fox, Sanek, LipSheZ, Possessed-by-zeal.

Medium Projects

HellDukeTC! will make your doom become alive, as the thread name calls it. My main purpose is to create Doom with a different angle and of course my secret recipe. As well as aiming to have a doom theme, we will also introduce you what hell actually means. It is still under development, however it is playable enough with it's satisfying levels, new enemies, new additions, new WEAPONS!, new HUD, CON scripted EVENTS, and much more. And last but not least, extra information can be found at hellreadme.txt. If you have any questions, you can ask me, XTHX2, and contact me. If you like Doom, and if you like challenges, this TC is just what you are in need of!

Duke Theft Auto is based upon the classic DMA/Rockstar game, "Grand Theft Auto" Run, Shoot, Kill, Car Jack your way through many cities on your way of becoming the number one criminal!
Duke Theft Auto on ModDB

A TC that changes Duke Nukem 3D into an exaggerated army-style shooter with various multiplayer additions (CTF, Hill Defend, Assault). Main focus is multi-player (though 1 playable single-player episode is included) and the massive unrealistic use of gore elements to turn the TC in kind of a "splatter game". Gameplay footage

Duke Nukem: Weapon of Mass Destruction is a gameplay mod for Duke Nukem 3D. It has tons of new weapon modes, enemies, and player abilities, such as UT style dodge moves, spinning hook kicks, and a Duke bot companion who fights by your side. In some levels you can even get in your skycar and fly it, doing bombing runs on enemies. In DNWMD, Duke collects glowing coins from slain enemies which are used to purchase various upgrades via a mouse controlled menu. In addition, each of Duke's weapons has its own experience level which increases with use.

Nuclear showdown is a gameplay mod for Duke Nukem that adds many features such as new weapons, enemies, effects to the default game as well as usermaps - it is built so you can play your favourite usermaps with, even ones that use custom art. You can also play through Duke It Out In D.C. if you have it. The TC also includes several features for mappers like more keycards, items such as the spacesuit and toolkit, and more textures to work with.